Fire retardant wood preserving composition



FIRE RETARDANT WOOD PRESERVIN G COMPOSITION N Drawing. Application May 18, 1953, Serial No. 355,873

4 Claims. o1. 16738.6)

This invention relates to the preservation of Wood, and to a composition which may be applied to the wood for that purpose, and which composition is characterized by its resistivity to combustion, whereby the fire hazard which is inherent in prior compositions is minimized. The invention further relates to a method of treating wood, such as a standing pole or timber, by the conjoint use of combustible and practically incombustible' preservative solutions, with provision for isolating from each other the portions of the wood treated by each composition.

It has heretofore been proposed to apply solutions of fungicides in oil to electric power transmission line poles, telephone poles, wooden bridge timbers, andthe like, to prolong the life of the wood and to increase its resistance to decay. A five per cent solution of pentachlorophenol in fuel oil is a known example of a preservative, and it is simply applied to the timber and allowed to penetrate, thereby impregnating the outer layer of the wood with the fungicide. Due to the inflammability of the oil, a serious fire hazard is created, particularly, for example, with pole lines extending for miles through forests, where constant inspection is economically impractical. Disruption of service, as the result of a fire, is a serious matter to the utility company maintaining the pole line, and also to the customers who utilize the service. When preservatives incorporating fuel oil, kerosene, and other petroleum oils are employed, this fire hazard persists for months after the solution is applied, as the oil evaporates very slowly.

Suggestions have been advanced to substitute noninflammable chlorinated solvents for petroleum oil, but these have not proved practical. The chlorinated hydrocarbons in general, and particularly those of higher chlorine substitution and larger carbon chains, are poor primary solvents for such preservative materials as the polychlorophenols. They are moreover relatively expensive. When the degree of chlorination is low, derivatives of the methane, ethane, ethylene, or propylene groups, for example, of evaporation are such that they are lost from the preservative composition before adequate penetration of the wood can be obtained. As is well understood, the preservative must penetrate below the'surface if the treatment is to be effective. Mixtures of these same, and technically pure, chlorinated hydrocarbons with petroleum products as vehicles for the fungicide are also unsatisfactory. The chlorinated compounds volatilize preferentially, leaving a residue of highly inflammable oil, and, as just noted, such mixtures may be deficient in solvent power, so that there is an inadequate concentration of fungicide for successful one-coat treatment.

Despite these recognized defects in the stated chlorinated hydrocarbons as solvents or blending agents for wood preserving compositions, I have discovered a combination of ingredients, which are believed to be also chlorinated hydrocarbons for the most part, and which do not have the disadvantages outlined above. This combination, which will be described herein as fully as present understanding permits, may be obtained as a volatilize too rapidly. Their rates nite States Patent residue in the production of trichloroethylene or tetrachloroethane.

The Well known process of synthesizing these compounds is summarized by Faith, Keyes, and Clark in Industrial Chemicals, page 611 et seq., John Wiley and Sons, Inc., New York, 1950, and hence need not be set forth in detail here. In brief, chlorine and acetylene are reacted in the presence of a catalyst, such as antimony trichloride, to produce tetrachloroethane, and the products of the first reaction are then passed through a towerinto which is trickled milk of lime, with the production of trichloroethylene, calcium chloride, and water. The trichloroethylene may be recovered by distillation, and the residue has heretofore been sent to waste.

These authors indicate that a recovery of ninety per cent of theoretical is attainable, but this is not necessarily true. The reactions are uncontrollable in the sense of obtaining only one specific product. Symmetrical tetrachloroethane is the main reaction product sought for in the initial reaction, but at the same time, other higher liquid chlorinated hydrocarbons are formed, and which have higher boiling points than trichloroethylene (app. 87 C.). These are readily separated from the brine after withdrawal from the reaction tower, and they constitute the combination of substances which I have discovered to be a superior and fire retardant vehicle for wood preserving fungicides.

This material is not a single compound, nor a mixture of compounds which can be readily separated by simple distillation. Usually less than twenty-five per cent distills below the boiling point of pentachloroethane (160-162 C.). The remaining seventy-five per cent is somewhat variable in composition, as shown by distillation curves, although it is reasonably uniform when obtained from a plant operating on a consistent cycle. There are strong indications that the higher boiling fractions consist mainly of three and four-carbon chlorinated hydrocarbons, with multiple substitution of halogen. The usual boiling range of this fraction lies between 170 and 210 C. The lower boiling first twenty-five per cent may show wider deviations from a mean distillation curve than the residual seventy-five per cent, which is attributed to larger variations in the amounts of tetrachloroethylene (B. P. 121 C.), unreacted tetrachloroethane (B. P. l46 C.), and pentachloroethane (B. P. 162 C.). A typical distillation yielded the following results:

TABLE I Per cent distilled: Temp. C. 5 120145 10 120-155 15 160 20 -165 25 168:2 30 174:2 35 176:2 40 179:2 50 182:2 6O 183:2 70 184:2 80 :2 90 198:3 100 210+5 It will be seen at once that the gradual rise in boiling point is indicative of molecular ingredients containing more than two carbon atoms, with varying degrees of chlorination. No exhaustive chemical analysis of this residuehas ever been made, insofar as a literature search and inquiry in the industry has revealed. And, as the variations in distillation rates further indicate, the residue does not have a constant composition. Identification is therefore now best made by physical properties. Specific gravity measurements on a number of samples give an average value of 1.56:0.05, or approximately thirteen pounds per U. S. gallon, which of course is higher than trichloroethylene-S. G. 12.2 pounds per gallon.

This residue from the distillation of the trichloroethylene (and after separation from the waterand calcium chloride) is not, in itself, a strong primary solvent for such fungicides as pentt'tchlorophenol. Average solubility at 25 C. does not exceed 4.5%. While a solution of the fungicide in the liquid hydrocarbon residue may be employed under certain conditions, and without addition of other constituents, better results are usually obtained by incorporating other ingredients. Due to this low solubility, it is therefore helpful to make a concentrated solution of the fungicide, which can thereafter be diluted with the above described chlorinated hydrocarbon mixture. A variety of formulations for such concentrate will readily occur to those skilled in theart, and the following formula represents one Which has been used with satisfactory results:

Formula 1 Pounds Pentachlorophenol, tech., 95% purity 42 H. T. petroleum solvent 38 Diacetone alcohol 20 To make 100 The H. T." solvent is a petroleum solvent marketed at present by American Mineral Spirits Company, with room temperature, equivalent to 9.75 pounds per gallon.

A one hundred pound batch will therefore yield approximately ten gallons containing four pounds of pentachlorophenol'per gallon. These are convenient round figures for workmen to use in making more dilute solutions for application to Wood. For example, one gallon of concentrate mixed with nine gallons of the chlorinated hydrocarbon residue will produce, approximately, a solution containing 0.4 pound of pentachlorophenol per gallon, which is a satisfactory concentration for application to Wood. Other concentrations may, of course, be employed, having in mind the condition of the wood. In general, acceptable concentrations will range from 0.225 to 0.75 pound per gallon.

The foregoing formulation may, under certain conditions, develop a bloom on the surface of the wood, due to the evaporation characteristics of the vehicle and the relatively low solubility of the fungicide. It is therefore oftendesirable to add an auxiliary agent to prevent this phenomenon. A variety of anti-blooming agents are known, and they may comprise high boiling, low volatility, high fungicide solvency materials, such as pine oil, ester gums, special resinous materials, and some higher alcohols. The use of these materials is common in the art, and it is simply to be noted here that they may be included in the compositions with which this invention is concerned, with good results.

A treating solution formulated as described above has distinct advantages over conventional wood preservative solutions having a petroleum base. Among them is the fact it is fire retardant, and will not support combustion at any time after it is applied. It Will, of course, be understood that the solution does not render the wood incombustible or absolutely fireproof, because under a prolonged and reasonably intense flame, the preservative would be volatilized. However, at no time is the treated wood more susceptible to fire than the original wood, but, on the contrary, its resistance to combustion is greatly increased. Another advantage is that the composition has a satisfactory solvent power for the fungicide, and, due to the low evaporation rate, there is ample time for the solution to penetrate well belowthe surface of the wood, carrying into the pores a sufficient amount of preservative to protect the wood for an increased length of time.

Formula 2 Pounds Mineral spirits a 3.75 Anti-blooming agent 0.59 Pentachlorophenol concentrate 0.93 Chlorinated hydrocarbon distillation residue 3.38

To make one gallon weighing 8.65

' The mineral spirits employed in this composition comprise petroleum fractions having a specific gravity of 0.780.79, flash point of 100-110 F., and distillation property of not less than below 350 F. (177 C.), and an end point of not more than 410 F. (210 C.). Referring to Table I, it will be seen that these fractions have distillation curves approximating that of the chlorinated distillation residue, and that the mineral spirits has a lower boiling point range than the H. T. solvent employed in Formula 1. This permits the use of the lower boiling fractions, when blended with the chlorinated residue, as the residue effectively masks the vapors of spirits, rendering them less susceptible to ignition. Adequate penetration is also obtained. The proportions of the ingredients may, of course, be varied, depending upon the condition of the wood, type of usual fungus and insect attack, and considerations of cost.

The anti-blooming agent ncorporated in the foregoing compositions may be any of thosenoted above. In this particular example, a high boiling alcohol, marketed by Monsanto Chemical Company as Sterox No. 110, was employed. It will also be noted that the pentachlorophenol concentration in this formulation is close to that in Formula 1, asthis has been found to be the optimum for a majority of applications.

A simple mixture of mineral spirits and chlorinated residue, in approximately equal parts by weight, will tend to ignite if exposed to a flame immediately after application to 'Wood. However, after a few hours, depending on temperature and wind velocity, the more volatile constituents of the mineral spirits evaporate, and the vapors are no longer combustible. At temperatures of say -75 F. and low windvelocity, this period of possible inflammability has not been found to exceed a day. It is entirely possible, when economic considerations do not offset potential hazard of fire, to distill the mineral spirits before making the composition, thereby further reducing the period of fire risk.

The ratio of mineral spirits to chlorinated residue may be varied from the approximately one to one ratio given above, to three to one or Zero to one. Above the three to one ratio, no significant reduction in inflammability is realized. When no mineral spirits are included, then the solution is incombustible from the outset.

Formula 3 Pounds Pentachlorophenol 0.37 Chlorinated hydrocarbon residue 3.70 Mineral spirits 3.83 Anti-blooming agent 0.75

rachlorophenol, trichlorophenol, 2-chloro-o-phenylphenol, and metal salts of the compositions termed naphthenic acids, such as copper, zinc, or iron naphthenate. The compositions may be applied to the wood in any of the known ways, as by brushing, dipping, soaking, spraying, and by vacuum or pressure processes.

A new method of wood treatment which utilizes the advantages of the fire retardant compositions has been developed for standing poles, timbers, and boards. For reasons of economy, it is usually not desirable to treat the entire timber, such as a utility pole which may be fifty or more feet in height above the ground line. Rights of way are usually kept reasonably free of tall vegetation for several yards on each side of the pole line, and hence flame heights, as may occur with a brush fire, are unlikely to reach up more than from five to ten feet. Accordingly, if the wood is treated to this height with the fire retardant solution, there is reasonable insurance against serious damage.

The area above the selected elevation may then be treated with the less costly usual fuel oil-fungicide solutions, but which, as noted at the outset, are readily inflammable. It becomes necessary, therefore, to isolate the upper and lower sections, to prevent the inflammable oil from running or seeping down into the lower section, and thus detracting from the benefits of the fire retardant treatment. A suitable liquid flow stop device may be made from a strip of oil absorbent material, such as natural or cellulose sponge, paper or textile wadding, felt, or the like. This is bound tightly, as a bandage, at the selected elevation, by means of a metal spring or a strap or belt which can be elfectively taken up. The sections are then treated with the respective solutions, for protection against decay and fire.

It will thus be seen that the present invention provides new and improved wood preserving compositions, which, in addition to providing for adequate concentration of preservative in the solution, also safeguard the wood from fire. This may be accomplished at a relatively slight increase in cost of materials over the use of highly hazardous compositions, and which cost increase constitutes economically justified, low premium, insurance. The attainment of these results is made possible by my discovery of the efiicacy of a mixture of chlorinated hydrocarbons whose distillation range, for the most part, is above the boiling points of the simpler chlorinated hydrocarbons. More particularly, the mixture which I have found suited is the dehydrated liquid residue from the preparation of trichloroethylene from tetrachloroethane by a distillation process. However, it will be apparent that high-carbon chlorinated hydrocarbon mixtures, which are solvents for fungicides, and are capable of suppressing the inflammability of petroleum fractions,

may be synthesized or obtained from other sources, and employed for the present purposes. It is therefore intended that the foregoing description should be taken as explanatory of the principles of the invention, and that it be accorded a scope commensurate with the following claims.

I claim:

1. A composition useful for the preservation of wood by application to the surface thereof comprising a solution of an oil soluble fungicide in a vehicle containing a substantial amount of liquid chlorinated hydrocarbons derived by dehydrating the residue remaining from the conversion of tetrachloroethane to trichloroethylene by the distillation process.

2. A composition useful for the preservation of wood by application to the surface thereof, comprising a solution of an oil soluble fungicide in inflammable petroleum solvent and a mixture of non-inflammable liquid chlorinated hydrocarbons, said chlorinated hydrocarbons being those derived by dehydrating the residue remaining from the conversion of tetrachloroethane to trichloroethylene by the distillation process, a substantial portion of said chlorinated hydrocarbons having a distillation range between C. and 210 C., the proportion of petroleum solvent to chlorinated hydrocarbons being not more than three to one by weight.

3. A composition as set forth in claim 2, wherein the petroleum solvent comprises mineral spirits.

4. A composition useful for the preservation of Wood by application to the surface thereof comprising a solution of a polychlorophenol in a mixture of mineral spirits and a plurality of liquid chlorinated hydrocarbons, said chlorinated hydrocarbons being derived from the conversion of tetrachloroethane to trichloroethylene by the distillation process, a substantial proportion of said chlorinated hydrocarbons having a distillation range between 165 C. and 210 C., the ratio of mineral spirits to said liquid chlorinated hydrocarbons being such that the solution and vapors emanating therefrom are noninflammable a short time after application to the wood, the polyehlorophenol being present in a concentration between 0.225 to 0.75 pound per gallon.

References Cited in the file of this patent UNITED STATES PATENTS 914,300 McElroy Mar. 2, 1909 1,482,416 Snelling Feb. 5, 1924 2,172,698 Clayton Sept. 12, 1939 2,182,081 Hatfield Dec. 5, 1939 

1. A COMPOSITION USEFUL FOR THE PRESERVATION OF WOOD BY APPLICATION TO THE SURFACE THEREOF COMPRISING A SOLUTION OF AN OIL SOLUBLE FUNGICIDE IN A VEHICLE CONTAINING A SUBSTANTIAL AMOUNT OF LIQUID CHLORINATED HYDROCARBONS DERIVED BY DEHYDRATING THE RESIDUE REMAINING FROM THE CONVERSION OF TETRACHLOROETHANE TO TRICHLOROETHYLENE BY THE DISTILLATION PROCESS. 